1. Field of Invention
The present disclosure relates to a light bar. More particularly, the present disclosure relates to a light bar in a direct type backlight module.
2. Description of Related Art
An LED (light-emitting diode) back-lit LCD (liquid crystal display) display is a flat panel display which uses LEDs as a backlight source. LED back-lit techniques can be categorized as direct back-lit (or full LED array back-lit) technique and edge-lit technique. The direct back-lit technique arranges a plurality of LEDs into an array and disposes the array behind optical films and an liquid crystal panel for directly illuminating the liquid crystal panel. Therefore, once the direct back-lit technique is adopted, brightness of different LEDs can be fine-tuned instantly according to gray scale variations of different parts in an image picture, and the dynamic contrast ratio is greatly enhanced, even to the standard of plasma displays.
Because applicable width of a fiber glass-reinforced epoxy laminate (for example, RF4 laminate) is much wider, it becomes a preferred substrate material of light bars in direct type backlight modules. However, due to its lower heat-dissipating coefficient, heat-dissipating conditions of different areas on a light bar substrate are inconsistent, so that thermal deformations of different areas on the substrate are different as well, which finally results in bending of the substrate.
Moreover, bending of the substrate further induces the LEDs to deviate from originally designed positions and deflects illuminating directions of the LEDs. Therefore, when the LEDs illuminate the liquid crystal panel for displaying picture images, inhomogeneous brightness of the picture images is shown, which then results in mura phenomena exhibiting traces or shadows.